this new book, the exhaustive work of columbia university professor manning marable, outlines why the investigation should be open. marable died last week, just before publication. why is it important that all these years later the investigation be reopened? >> it is important because professor marable believed in justice and his killers were never served justice. >> reporter: february 21, 1965, malcolm x was speaking to several hundred people at a ballroom in harlem when suddenly three men stood up in the front rows and opened fire. thomas hagen was caught at the scene and confessed to being one of the gunmen. 12 years later, he signed affidavits claiming two other men who both served long prison sentences had nothing to do with the shooting. >> as marable's quite powerful book details, four of the actual assassins never were pursued and at least one of them still lives openly in the metro new york area. >> reporter: the book claims the n.y.p.d. knew malcolm x's life was in danger but turned the other way in the face of threats. by almost any standard, the investigation here at the m